Linear variable differential transformers (LVDTs) are electromechanical transducers that convert rectilinear motion of externally coupled objects into electrical signals that are proportional to the positions of the objects. LVDTs have been utilized in conjunction with a wide range of measurement and control devices such as flowmeters, strain gages, and pressure sensors. Important characteristics of a practical LVDT include (i) the ability to produce a linear output signal over a relatively large displacement range relative to the overall length of the device, (ii) durability and reliability, and (iii) relatively low cost of manufacture.
Generally, in LVDTs a single primary winding is excited by a single-phase input signal in such a manner that there occurs, at individual locations of two differentially-connected secondary windings, reluctance that varies in response to a varying linear position of an iron core (which moves with an object of detection) so that the voltage amplitude level of a resultant single-phase inductive AC output signal indicates the linear position of the iron core. Such LVDTs are capable of detecting a linear position over a range where the induced voltage value shows linearity with respect to the linear position of the core, at and around the locations of the two secondary windings. The windings are provided in such a manner that the induced voltage varies in a differential manner, and the function of variation in the induced voltage value relative to the linear position does not change over a periodic function (e.g., a trigometric function such as a sine function).
Position accuracy provided by conventional LVDTs is generally constant throughout the range of motion of the core within the LVDT. While this may be sufficient for typical LVDT applications, it may be desirable to enhance the accuracy of the LVDT's position sensing capabilities, particularly at certain locations within the stroke of the LVDT.